Polycarbonates obtained from aromatic dihydroxy compounds are known and, because of their interesting technological properties, have found acceptance in many fields of use. However, their sensitivity to organic solvents and stress cracking is still a certain disadvantage in specific applications.
Polycarbonates which carry methyl substituents (German Published Patent Specification No. 2,063,050) which corresponds to U.S. Pat. No. 3,879,348, halogen substituents (U.S. Pat. No. 3,062,781) or unsaturated substituents (U.S. Pat. No. 3,692,870) on the aromatic ring are already known in the art.
It is also known in the art to cross-link special polycarbonates with electron rays (see German Published Patent Specification No. 2,615,038 and the corresponding U.S. Pat. No. 4,129,612.
It has now surprisingly been found that thermoplastic aromatic polycarbonates containing aromatically bonded halogen, primary alkyl, secondary alkyl and/or alkenyl substituents can be modified by irradiation with UV light, after adding between about 1 and 5% by weight, preferably between about 1 and 3% by weight, relative to the weight of polycarbonate, of photoinitiators, so that they acquire an outstanding resistance to organic solvents and a high resistance to stress cracking. Furthermore, the modified polycarbonates can be rendered extremely flame-resistant (VO according to UL Subject 94) in a simple manner by admixing a flameproofing agent before the UV irradiation.